Application of cas protein, method for detecting target nucleic acid molecule and kit

ABSTRACT

The present invention provides use of a Case protein, and a method and a kit for detecting target nucleic acid molecules. The method for detecting target nucleic acid molecules comprises adding a guide RNA, a Cas12a, and a nucleic acid probe into a reaction system containing target nucleic acid molecules to be detected, and detecting it after the reaction is completed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation application of U.S. application Ser. No. 17/224,541, filed Apr. 7, 2021, which is a continuation of U.S. application Ser. No. 16/631,157, filed Jan. 14, 2020 which is a national stage filing under section 371 of International Application No. PCT/CN2018/82769, filed on Apr. 12, 2018, and published on Jan. 17, 2019 as WO 2019/011022, which claims priority to Chinese Application No. 201710573752.0, filed on Jul. 14, 2017. The entire contents of each of these priority applications are hereby incorporated herein by reference.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on May 6, 2020, is named 2013065-0286_SL.txt and is 56,958 bytes in size.

TECHNICAL FIELD

The present invention belongs to the field of biotechnology, and in particular, the present invention relates to a method for the detection of target nucleic acid molecules.

BACKGROUND

Specific detection method of nucleic acids has important values in applications such as pathogen detection, genetic disease detection and the like. For pathogen detections, because each pathogenic microorganism has its unique characteristic nucleic acid sequences, the detection of nucleic acid molecules for specific species can be developed, also known as nucleic acid diagnostics (NADs), plays an important role in the field of food safety, environmental microbial pollution detection, human pathogen infections and the like. In another aspect, the NAD methods can also detect single nucleotide polymorphisms (SNPs) in human beings or other species. Understanding the relationship between genetic variation and biological function at the genomic level may provide a new perspective for modern molecular biology, among which SNPs are closely related to biological function, evolution, disease and the like, thus the development of techniques for detection and analysis of SNPs is particularly important.

So far, several NAD methods have been established, most of which are created for the detection of specific DNA molecules and some of which are for RNA molecules. Usually, DNA molecules are very stable and detection samples can be from a series of complex biological samples, while RNA molecules can be easily degraded and should be treated with care. In 1970s, restriction endonuclease digestion detection methods were developed, and then by the development of methods for detection of specific nucleic acid molecules such as Southern, Northern and dot hybridization. In 1985 when the PCR method became a routine experimental method, it led to exponential progress in molecular biology. The detection of specific nucleic acid molecules currently established usually requires two steps, the first step being target nucleic acid amplification and the second step being target nucleic acid detection. PCR technique is the first established and currently most commonly used amplification method. Based on the PCR method, fluorescence labelled probes are introduced to facilitate realtime detection of the amplification of target (named as Realtime PCR), which is a rapid and highly sensitive detection method and can be used for quantitative analysis. Besides of PCR amplification method, many alternative methods have been created, such as the ligase chain reaction, the branched DNA amplification, NASBA, SDA, transcription-mediated amplification, loop-mediated isothermal amplification (LAMP), rolling circle amplification (RCA), Recombinase Polymerase Amplification (RPA) and the like. The advantage of these alternative methods lies in the isothermal characteristic, that's to say that the reaction can be simply accomplished at one temperature, without the need for thermal cycling instruments for PCR. In addition to real-time PCR, which can directly complete amplification and detection, among nucleic acid detection methods, FISH hybridization technology (Fluorescence in situ hybridization), the most commonly used detection method, hybridizes in situ with complementary target sequences by labeling molecular probes. In addition, detection methods such as next-generation sequencing technologies and Oxford Nanopore sequencing technologies have also been developed, but these methods usually require expensive experimental equipment.

The detection of SNPs first also needs to be amplified by PCR and other methods to obtain enough amounts of fragments containing SNP site regions for further detection. Common approaches include primer extension, hybridization, ligation and enzymatic cleavage. After completing the above methods, you need to use specific methods for detection, such as mass spectrometry detection, fluorescence detection, chemiluminescence detection, etc.

Although many detection methods have been developed as described above for nucleic acid detection, in some cases, faster, simpler and cheaper detection is still an important development direction, such as rapid detection of pathogens in the wild, rapid detection of drug-sensitive SNPs, etc. In 2016, Collins et al. developed a rapid and inexpensive method for detecting Zika virus based on the characteristics of CRISPR-Cas9 that specifically recognizes and cleaves target sequences. In 2017, Zhang Feng et al. took advantage of the collateral effect of CRISPR-Cas13a to build a rapid nucleic acid detection method. “Collateral effect”, i.e., Cas13a binds to specific target RNA and then randomly cleaves other non-target RNAs (here, the RNA molecule is designed as an RNA fluorescence reporter system), combined with isothermal amplification technology RPA to achieve rapid target RNA detection; and Zhang Feng team called this detection method as SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing). The SHERLOCK method involves the binding of RNA templates, so if you need to detect DNA, DNA should be first transcribed to RNA for detection; in view of the instability of RNA, this method will undoubtedly increase the difficulty of operation.

In 2015, Zhang Feng et al. discovered a new CRISPR-associated protein endonuclease Cas12a (formerly known as Cpf1), which is an RNA-guided specific DNA endonuclease like the commonly used Cas9 protein; but compared with Cas9, Cas12a has its own characteristics, such as the need for crRNA to guide the specific cleavage of double-stranded DNA and produce cohesive ends.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for detecting target nucleic acid molecules.

Another object of the present invention is to provide a use of a Cas protein in a method for detecting target nucleic acid molecules.

In a first aspect of the invention, provided is a kit, comprising a guide RNA, a Cas protein, a nucleic acid probe and a buffer.

provided is a method for detecting target nucleic acid molecules, which comprises adding a guide RNA, a Cas protein, a nucleic acid probe and a buffer into the reaction system containing the target nucleic acid molecules to be detected, and then detecting the target nucleic acid molecules (especially by detection of the fluorescence intensity).

Preferably, the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a.

Preferably, the Cas protein is Cas12a.

The Cas12a is preferably one of FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a or Lb4Cas12a.

Preferably, the Cas12a is LbCas12a.

Preferably, the guide RNA refers to an RNA that directs the Cas protein to specifically bind to the target DNA.

In another preferred embodiment, the nucleic acid probe is a single-stranded DNA; the single-stranded DNA is preferably a fluorescently labelled single-stranded DNA; and the single-stranded DNA is preferably a fluorescent probe labelled with a fluorescent group HEX at the 5′ end and a quenching group BHQ1 at the 3′ end.

In another preferred embodiment, the detection method of the nucleic acid probe is preferably a fluorescence detection method; and the fluorescence detection method is preferably by using a microplate reader or a fluorescence spectrophotometer.

Preferably, the target nucleic acid molecules to be detected in the reaction system of the target nucleic acid molecules to be detected are obtained after amplification.

Preferably, the detection method of the present invention can detects pathogenic microorganisms, gene mutations or specific target DNA.

In another preferred embodiment, the Cas protein comprises Cas12b (C2c1).

In a second aspect of the invention, provided is a use of a Cas protein in a method for detecting target nucleic acid molecules, or for preparing a preparation for the detection of target nucleic acid molecules.

In another preferred embodiment, when the target DNA, the guide RNA and the Cas protein form a ternary complex, the complex cleaves other single-stranded DNA molecules in the system.

Preferably, the guide RNA refers to an RNA that directs the Cas protein to specifically bind to the target DNA.

In a third aspect of the invention, provided is a kit comprising a guide RNA, a Cas protein and a nucleic acid probe.

In another preferred embodiment, the kit further comprises a buffer.

In a fourth aspect of the invention, provided is a detection system for detecting target nucleic acid molecules, comprising:

(a) a Cas protein, which is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a;

(b) a guide RNA, which directs the Cas protein to specifically bind to target nucleic acid molecules; and

(c) a nucleic acid probe, which is a single-stranded DNA;

Wherein the target nucleic acid molecule is a target DNA.

In another preferred embodiment, the detection system further comprises (d) a buffer.

In another preferred embodiment, the detection system further comprises target nucleic acid molecules to be detected.

In another preferred embodiment, the concentration of the target nucleic acid molecules to be detected in the detection system is from 1 to 100 copies/μL or 10¹⁵ copies/μL, preferably from 1 to 10 copies/μL, more preferably from 1 to 5 copies/μL.

In another preferred embodiment, in the detection system, the molar ratio of the nucleic acid probe to the target nucleic acid molecule is from 10³:1 to 10¹⁴:1, preferably from 10⁴:1 to 10⁷:1.

In another preferred embodiment, the detection site of the target nucleic acid molecule is located at positions 1-12 downstream of the PAM sequence of the guide RNA.

In another preferred embodiment, the length of the guide RNA is 15-30 nt, preferably 15-18 nt.

In another preferred embodiment, the target DNA comprises cDNA.

In another preferred embodiment, the target DNA is selected from the group consisting of: single-stranded DNA, double-stranded DNA, or a combination thereof.

In another preferred embodiment, the nucleic acid probe has a fluorescent group and a quenching group.

In another preferred embodiment, the fluorescent group and the quenching group are each independently located at the 5′ end, the 3′ end, and the middle of the nucleic acid probe.

In another preferred embodiment, the length of the nucleic acid probe is from 3 to 300 nt, preferably from 5 to 100 nt, more preferably from 6 to 50 nt, and most preferably from 8 to 20 nt.

In another preferred embodiment, the target nucleic acid molecules comprise target nucleic acid molecules derived from a species selected from the group consisting of: a plant, an animal, an insect, a microorganism, a virus, or a combination thereof.

In another preferred embodiment, the target DNA is a artificially synthesized or a naturally occurring DNA.

In another preferred embodiment, the target DNA comprises a wild-type or a mutant DNA.

In another preferred embodiment, the target DNA comprises DNA obtained by RNA reverse transcription or amplification, such as cDNA and the like.

In another preferred embodiment, the Cas12a is selected from the group consisting of: FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a, Lb4Cas12a or a combination thereof; more preferably, the Cas12a is LbCas12a.

In another preferred embodiment, the Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a is selected from the group consisting of: Cas12b (i.e., C2c1).

In another preferred embodiment, the Cas12b protein is selected from the group consisting of: AacCas12b (Alicyclobacillus acidoterrestris), Aac2Cas12b (Alicyclobacillus acidiphilus), AkCas12b (Alicyclobacillus kakegawensis), AmCas12b (Alicyclobacillus macrosporangiidus), AhCas12b (Alicyclobacillus herbarius), and AcCas12b (Alicyclobacillus contaminans).

In another preferred embodiment, the nucleic acid probe comprises a single-stranded DNA with a detectable label.

In another preferred embodiment, the single-stranded DNA is a single-stranded DNA labelled with fluorescence and biotin.

In another preferred embodiment, the single-stranded DNA is a single-stranded DNA labelled with fluorescence.

In another preferred embodiment, the single-stranded DNA is a fluorescent probe labelled with a fluorescent group HEX at the 5′ end and a quenching group BHQ1 at the 3′ end.

In a fifth aspect of the invention, provided is a kit for detecting target nucleic acid molecules, comprising:

i) a first container and a Cas protein located in the first container, wherein the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a;

ii) optionally a second container and a guide RNA located in the second container, wherein the guide RNA directs the Cas protein to specifically bind to the target nucleic acid molecules;

iii) a third container and a nucleic acid probe located in the third container;

iv) optionally a fourth container and a buffer located in the fourth container;

Wherein the target nucleic acid molecule is a target DNA.

In another preferred embodiment, any two, three, or four (or all) of the first, second, third, and fourth container may be the same or different container.

In another preferred embodiment, the nucleic acid probe has a fluorescent group and a quenching group.

In a sixth aspect of the invention, provided is a method for detecting whether target nucleic acid molecules are present in a sample, charcterized by comprising the steps of:

(a) providing a detection system for detecting target nucleic acid molecules according to the fourth aspect of the invention, and the detection system further contains a sample to be detected; and

(b) detecting whether the nucleic acid probe in the detection system is cleaved by the Cas protein, wherein the cleavage is a trans-cleavage of the collateral single-stranded DNA;

Wherein, if the nucleic acid probe is cleaved by the Cas protein, it indicates that the target nucleic acid molecule is present in the sample; and if the nucleic acid probe is not cleaved by the Cas protein, it indicates that the target nucleic acid molecule is not present in the sample.

In another preferred embodiment, the sample to be detected comprises an unamplified sample and an amplified (or nucleic acid amplified) sample.

In another preferred embodiment, the sample to be detected is a sample obtained by amplification.

In another preferred embodiment, the nucleic acid amplification method is selected from the group consisting of: PCR amplification, LAMP amplification, RPA amplification, ligase chain reaction, branched DNA amplification, NASBA, SDA, transcription-mediated amplification, rolling circle amplification, HDA, SPIA, NEAR, TMA and SMAP2.

In another preferred embodiment, the PCR comprises high temperature PCR, normal temperature PCR, and low temperature PCR.

In another preferred embodiment, the method is for detecting whether there is an SNP, a point mutation, a deletion, and/or an insertion for nucleic acids at a target site.

In another preferred embodiment, when the PAM sequence is absent at the upstream or downstream of the target site (in the range of from −20 nt to +20 nt, preferably in the range of from −15 nt to +15 nt, and more preferably in the range of from −10 nt to +10 nt), nucleic acid amplification was carried out using primers introduced with PAM.

In another preferred embodiment, the primer introduced with PAM has a structure of formula I from 5′ to 3′:

P1-P2-P3   (I)

wherein,

P1 is a 5′ segment sequence complementary or non-complementary to the sequence of the target nucleic acid molecule at the 5′ end;

P2 is a PAM sequence; and

P3 is a 3′ segment sequence complementary to the sequence of the target nucleic acid molecule at the 3′ end.

In another preferred embodiment, the PAM primer specifically binds upstream or downstream of the target nucleic acid molecule.

In another preferred embodiment, P1 has a length of 0 to 20 nt.

In another preferred embodiment, P3 has a length of 5 to 20 nt.

In another preferred embodiment, the PAM primer has a length of 18 to 50 nt, preferably 20 to 35 nt.

In another preferred embodiment, the complementation comprises full complementation and partial complementation.

In another preferred embodiment, at least one primer with a PAM sequence is used in the nucleic acid amplification.

In another preferred embodiment, when the PAM sequence is present at the upstream or downstream of the target site (in the range of from −20 nt to +20 nt, preferably in the range of from −15 nt to +15 nt, and more preferably in the range of from −10 nt to +10 nt), primers with or without a PAM sequence can be used, and the amplified amplification product contains the PAM sequence.

In another preferred embodiment, the detection in step (b) comprises a fluorescence detection method.

In another preferred embodiment, a microplate reader or a fluorescence spectrophotometer is used in the fluorescence detection method.

In a seventh aspect of the invention, provided is a use of a Cas protein for the preparation of a detection reagent or kit for detecting target nucleic acid molecules based on a collateral single-stranded DNA cleavage, wherein the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a.

In another preferred embodiment, the Cas12a is selected from the group consisting of: FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a, Lb4Cas12a or a combination thereof; more preferably, the Cas12a is LbCas12a.

In another preferred embodiment, the Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a is selected from the group consisting of: Cas12b (or C2c1).

In another preferred embodiment, the Cas12b protein is selected from the group consisting of: AacCas12b.

It should be understood that within the scope of the present invention, the various technical features of the present invention above and the various technical features specifically described hereinafter (as in the Examples) may be combined with each other to constitute a new or preferred technical solution. Due to space limitations, it is not repeated here.

DESCRIPTION OF FIGURE

FIG. 1A-G shows the cis-cleavage characteristics of the Cas12a cleaving target single-stranded DNA. FIGS. 1C and 1D discloses SEQ ID NOS 3 and 3, respectively, in order of appearance.

FIG. 2A-B shows Cas12a cleaves target single-stranded DNA independent of PAM sequence required for cleaving double strands. FIG. 2B discloses SEQ ID NOS 3, 11, 13, 12, 1, 3, 14, 11, 16, 13, 15, and 12, respectively, in order of appearance.

FIG. 3A-D shows the trans-cleavage characteristics of the Cas12a cleaving single-stranded DNA.

FIG. 4A-D shows 10 different sources of Cas12a tested, all of which have cis- and trans-cleavage activity for single-stranded DNA.

FIG. 5A-D shows through Cas12a single-point mutation experiment, the sites in Cas12a that may be related to the cis- and trans-cleavage activity of single-stranded DNA were identified.

FIG. 6 shows the structures of Cas12a and Cas12b (i.e., C2c1) monomers and their complexes with guide RNA and target DNA.

FIG. 7 shows different Cas12a uses specific double-stranded DNA substrates and single-stranded DNA (HEX-N12-BHQ1) as the fluorescent detection probe to obtain the fluorescence value. The negative control group does not add specific substrates. No specific substrate added was employed as the negative control group.

FIG. 8 shows schematic of target DNA detection by the HOLMES method based on target DNA amplification and Cas12a trans-cleavage activity against collateral single-stranded DNA.

FIG. 9A-B shows sensitivity test of target DNA by direct use of FnCas12a or LbCas12a, or in combination of the HOLMES method.

FIG. 10A-B shows fluorescence detection value of the HOLMES method using crRNAs with different lengths of the guide sequence combined with FnCas12a or LbCas12a on target sequences with different single point mutations.

FIG. 11A-B shows using FAM-labeled fluorescent probes, 10 Cas12a proteins were selected to test whether the FAM-labeled single-stranded DNA probe is trans-cleaved after adding the target single-stranded DNA.

FIG. 12 shows using HEX-N12-BHQ1 as a probe, 10 Cas12a proteins were selected to test the fluorescence value after adding the target single-stranded DNA.

FIG. 13A-B. (A) Single-stranded DNA fluorescent probes labeled with HEX and BHQ1 at both ends show HOLMES detection values using the gyrB gene fragment as the target sequence and different concentrations of pure cultured E. coli MG1655 as the positive control template. It is shown that as the concentration of E. coli MG1655 decreases, its fluorescence response value gradually decreases. (B) Detection values of environmental water samples in different locations.

FIG. 14A-F shows schematic diagram of the HOLMES method for detecting SNPs, and the fluorescence detection values of 5 SNP sites.

FIG. 15 shows the fluorescence detection values in key sites when using HOLMES method for detecting TP53 gene (a cancer-related gene).

FIG. 16A-E shows the detection values of 5 SNP sites (gout related) by using HOLMES method.

FIG. 17 shows the detection values of 1 SNP site (gout related) by using HOLMES method, with samples from 21 volunteers.

FIG. 18 shows a scheme for primers design in one Example of the present invention, which could be used for HOLMES detection of SNP in any site.

FIG. 19A-B shows the detection of E. coli with the combination of LAMP and HOLMES in the system. (A) The electrophoretogram of the E. coli gyrB gene amplified by LAMP. Two groups of primers (i.e. gyrB-1 and gyrB-2) were used to amplify the gyrB gene, which is the informative gene of E. coli. (B) Detection of the LAMP amplification products with HOLMES detection system. Negative control: The sample was sterilized water, and the gyrB gene was amplified or the result thereof was detected with gyrB-1 amplification primers. gyrB-1: The sample was the E. coli to be detected, and gyrB gene was amplified or the result thereof was detected with the first group of gyrB gene amplification primers. gyrB-2: The sample was the E. coli to be detected, and gyrB gene was amplified or the result thereof was detected with the second group of gyrB gene amplification primers.

FIG. 20A-B shows the detection of the genotypes of human HEK293T cells through the combination detection of LAMP and HOLMES. (A) The electrophoretogram of SNP detection template corresponding to human HEK293T amplified by LAMP. Negative control: The sample was sterilized water, and the amplification result was detected with rs5082 amplification primers. rs5082: The sample was the total genomic DNA from human HEK293T cells, and the amplification result was detected with rs5082 amplification primers. rs1467558: The sample was the genomic DNA from human HEK293T cells, and the amplification result was detected with rs1467558 amplification primers. (B) Detection of the LAMP amplification product with HOLMES detection system. Two crRNAs, crRNA-G and crRNA-T were used for detection of the rs5082 site (Sequence Listing 5), respectively, and two crRNAs, crRNA-C and crRNA-T were used for detection of the rs1467558 site (Sequence Listing 5), respectively.

FIG. 21A-B shows the detection of E. coli with the combination of RPA and HOLMES in the system. (A) Amplification of the E. coli gyrB gene with RPA. Two groups of primers (i.e. gyrB-1 and gyrB-2) were used to amplify the gyrB gene, which is the informative gene of E. coli. (B) Detection of the RPA amplification products with HOLMES detection system. Negative control: The sample was sterilized water, and the gyrB gene was amplified or the result thereof was detected with gyrB-1 amplification primers. gyrB-1: The sample was the E. coli to be detected, and gyrB gene was amplified or the result thereof was detected with the first group of gyrB amplification primers. gyrB-2: The sample was the E. coli to be detected, and gyrB gene was amplified or the result thereof was detected with the second group of gyrB amplification primers.

FIG. 22 shows the detection of the collateral ssDNA cleavage activity of Cas12b with ssDNA as target DNA. After the collateral cleavage reaction, the reactants were subject to denatured gel electrophoresis separation with 12% urea and detected with the fluorescence imaging system. The number in the brackets stood for the final concentration, in nM, of reactants. The 50 nM ssDNA of 66 nts was used as the target DNA, and 50 nM 5′-end FAM-labelled ssDNA was used as the ssDNA probe. As shown in the figure, with the addition of Cas12b, guide RNA and target DNA, FAM-labelled ssDNA was cleaved into fragments, demonstrating that Cas12b had collateral ssDNA cleavage activity.

FIG. 23 shows the detection of the collateral ssDNA cleavage activity of Cas12b with ssDNA or dsDNA as target DNA. After collateral cleavage reaction was completed, the reactants were detected with a fluorescence microplate reader. The amount of Cas12b and guide RNA was 500 nM. 50 nM ssDNA (66-nt) or dsDNA (66-nt) was used as the target DNA. 500 nM ssDNA probe containing fluorescence reporter and quencher group (HEX-N12-BHQ1) was used as the ssDNA probe. As shown in the figure, upon the addition of Cas12b and guide RNA, no matter ssDNA template or dsDNA template, the collateral ssDNA cleavage activity could be detected.

FIG. 24 shows the collateral ssDNA trans-cleavage activity generated by Cas12b with the combination of LAMP amplification for low-concentration target DNA.

DETAILED DESCRIPTION

In order to make the aim, technical solution and advantages of the Examples of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the Examples of the present invention. Obviously, the Examples described herein are not all of the Examples of the present invention. All other Examples obtained by those skilled in the art based on the Examples of the present invention without creative efforts are within the scope of the present invention.

By extensively and intensively studies, the present inventors have developed a technical solution for target nucleic acid detection, by studying the cleavage properties of Cas enzymes such as Cas12a and Cas12b enzymes. The experimental results show that the above technical solutions are successfully used to rapidly detect nucleic acids. For example, identification of whether the water contains a certain concentration of microorganisms such as Escherichia coli and rapid identification of SNP genotypes are accomplished. On this basis, the present invention has been completed.

The terms

The term “guide RNA” refers to an RNA that directs the Cas protein to specifically bind to a target DNA sequence.

The term “crRNA” refers to CRISPR RNA, which is a short RNA that directs Cas12a to bind to a target DNA sequence.

The term “CRISPR” refers to clustered regular interspaced short palindromic repeats, which are the immune systems of many prokaryotes.

The term “Cas protein” refers to a CRISPR-associated protein which is a related protein in the CRISPR system.

The term “Cas12a” (formerly “Cpf1”) refers to a crRNA-dependent endonuclease, which is an enzyme of type V-A in the CRISPR system classification.

The terms “Cas12b”, and “C2c1” are used interchangeably and refer to a crRNA-dependent endonuclease, which is an enzyme of type V-B in the CRISPR system classification.

The term “LAMP” is a loop-mediated isothermal amplification technique and is a thermostatic nucleic acid amplification technique suitable for gene diagnosis.

The term “PAM” refers to a protospacer-adjacent motif, which is required for Cas12a cleavage. The PAM of FnCas12a is the sequence TTN, the PAM of LbCas12a is the sequence TTTN, and the PAM of AacCas12b is the sequence TTN.

The present invention provides a method for detecting target nucleic acid molecules, which comprises adding a guide RNA, a Cas protein, a nucleic acid probe and a buffer into the reaction system containing the target nucleic acid molecules to be detected, and then detecting the fluorescence intensity thereof

The Cas protein is Cas12a or Cas12b.

The Cas12a is preferably one of FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a or Lb4Cas12a; the Cas12a is preferably LbCas12a.

The Cas12b is preferably AacCas12b, Aac2Cas12b, AkCas12b, AmCas12b, AhCas12b, and AcCas12b.

The guide RNA refers to an RNA that directs the Cas protein to specifically target a DNA sequence.

The target nucleic acid molecules to be detected in the reaction system containing the target nucleic acid molecules to be detected are obtained after amplification.

The detection method detects pathogenic microorganisms, gene mutations or specific target DNA.

The present invention provides a use of a Cas protein in a method for detecting target nucleic acid molecules.

When the target DNA, the guide RNA and the Cas protein form a ternary complex, the complex cleaves other single-stranded DNA molecules in the system.

The guide RNA refers to an RNA that directs the Cas protein to specifically target a DNA sequence.

The invention also provides a kit, comprising a guide RNA, a Cas protein and a nucleic acid probe. Furthermore, the kit of the invention may further comprise a buffer.

The present invention provides a detection method for rapidly detecting target nucleic acid molecules with high specificity. Once the target DNA (single or double stranded), the crRNA, and the Cas12a protein form a ternary complex, the complex cleaves other single-stranded DNA molecules in the system. In the method, the target DNA (a DNA sequence to be detected) is targeted by the designed crRNA; and crRNA and Cas12a protein are added to the detection system. When the target DNA is present, Cas12a, the crRNA and the target DNA form a ternary complex, and the complex cleaves the single-stranded DNA with fluorescent signal label (the fluorescent group and the quenching group are respectively labelled to the two ends, and the fluorescent group can be luminescent after the DNA is cleaved) using its collateral cleavage activity, thereby emitting fluorescence. Therefore, by detecting the fluorescence, it is possible to know whether or not the target DNA molecule is contained in the system to be detected. The method of the present invention allows rapid detection of whether a sample contains a specific DNA sequence. By combining with PCR technology, the sensitivity of the detection method can be greatly improved. The nucleic acid probe in the present invention is preferably a fluorescent probe.

HOLMES Condition Test:

The invention provides the application of Cas12 enzyme based on Cas12a, Cas12b and the like in nucleic acid detection. The following describes Cas12a as an example.

Selection of Cas12a: According to the study, Cas12a has the activity of trans cleavage, ie, once the target DNA, crRNA and Cas12a protein form a ternary complex, other single-stranded DNA (collateral single-stranded DNA) in the system will be cleaved. A specific DNA detection method was designed based on this principle. Firstly, the collateral DNA was designed as a fluorescent probe consisting of a random sequence with a length of 12 nt, and labelled with the fluorescent group HEX at the 5′-terminal end and labelled with the quenching group BHQ1 (HEX-N12-BHQ1) at the 3′-terminal end. When the system contains the target DNA fragment, a ternary complex of the target DNA, crRNA and Cas12a protein will be formed. At this time, the probe is cleaved, and the fluorescence emitted from the HEX fluorescent group can be detected by the fluorescence detector (excitation at 535 nM, and emission at 556 nM). Secondly, 10 different Cas12a were tested, and the target sequence was double-stranded DNA, as shown in FIG. 7 . It can be seen that the complex composed of the target double-stranded DNA and each Cas12a protein can achieve trans cleavage activity.

HOLMES Response Sensitivity: Next, the sensitivities of FnCas12a and LbCas12a response to target DNA were tested. That is, the lowest concentration of target DNA that can respond was examined. As shown in FIG. 9 , when the test target was directly added, the target DNA with concentration above 0.1 nM was able to respond, and the response was significant at a concentration above 1 nM. If the PCR technique is combined (i.e. HOLMES method), as shown in FIG. 8 , i.e. the target fragment is first amplified by PCR and then subjected to Cas12a cleavage reaction, the response sensitivity can be as low as 10 aM, as shown in FIG. 9 .

SNP test: Next, whether the HOLMES method can detect the SNP genotype was tested. T1 was used as the target sequence, and mutations were introduced in the PAM or single point mutation was introduced in the target sequence at position of 1-18. And the difference between the non-mutated sequence and the mutant sequences was compared for the crRNAs of different lengths.

As shown in FIG. 10 , when the target complementary sequence is a 24 nt crRNA (crRNA-24 nt), the single point mutations at position of 8-18 are not significantly different from the wild type. When there is any mutation in the PAM and there is any point mutation at position of 1-7, there is a significant drop on the fluorescence value. When the crRNA was truncated and the length of the paired target sequence was 18 nt, the fluorescence value of the target sequence mutated at position 8-16 nt was significantly lower than that of the target sequence with a length of 24 nt. When the length was shortened to 16 nt or 17 nt, the decrease of fluorescence value of the target sequence after mutation was more obvious. When the length was shortened to 15 nt, the fluorescence values of the target sequence and the mutation are weak for the target sequence, but still strong for other target sequences, which can be used for detection. Taken together, 15 nt, 16 nt and 17 nt crRNAs are most suitable for detection of SNPs.

In the present invention, Cas12a cleaves single-stranded DNA. A programmed cleavage mode wherein Cas12a cleaves single-stranded DNA independent of PAM sequence is called cis cleavage; and once a ternary complex Cas12a/crRNA/target DNA is formed, it shows the activity of trans-cleavage, that is, the activity of cleavage of any non-target single-stranded DNA in the system.

Using the characteristics of Cas12a, a method for specifically detecting nucleic acid molecules has been developed, which is called HOLMES (one Hour Low-cost Multipurpose Efficient Simple assay). As the name of the technology, it is characterized as a fast (1 hour), low cost, multi-purpose, efficient, and simple method. The method can be used in the fields of rapid pathogen detection, SNP detection and the like.

Nucleic acid detection based on collateral cleavage activity

The invention also provides a method of nucleic acid detection based on the collateral cleavage activity of a Cas12 enzyme, including Cas12a or Cas12b.

Preferably, the detection of the invention can be performed on SNPs, in particular by PCR amplification followed by detection.

Referring to FIG. 18 , the design of the primers is given.

Case 1. When there is a PAM site near the SNP site, the synthesized crRNA based on the guide sequence designed according to the PAM site can be used for HOLMES detection. When the HOLMES method is used for detection, the background signal is relatively low; for the same guide sequence, the signal difference between different SNP templates is relatively large.

Case 2. When there is no PAM site near the SNP site, or there is no suitable PAM site, the introduction of the PAM site can be performed according to the above experimental protocol.

A typical procedure comprises designing a primer near the SNP site, carrying a PAM site on the primer, and the 3′ end sequence at the PAM site needs to be paired with the template DNA. There is no special requirements for the primer at the other end, and it only needs to be paired with the template DNA and can be subjected to PCR amplification. As shown in FIG. 18 , the PAM site was successfully introduced after PCR amplification.

Referring to FIG. 10 , in the present invention, when designing for the introduction of a PAM, usually the SNP site is located at the position of the first 16 bases of from 5′ end of the crRNA guide sequence, preferably 1-14, more preferably 1-12, more preferably 1-11 or 1-10, and most preferably 1-8 or 1-7.

The main advantages of the invention are:

(1) Fast: When the test conditions are ready, it takes only about 1 hour from getting the sample to getting the test result.

(2) Low cost: There are no special materials or enzymes required in the experiment, and the amount of materials and reagents involved is small. It can be used for testing and analysis of trace amounts.

(3) Efficient: The method of the present invention has extremely high sensitivity and can detect DNA at a concentration of 10 aM.

(4) Multi-purpose: It can detect different nucleic acid samples, including DNA samples and RNA samples.

(5) Simple: There are no special complicated steps. If the kit is ready and the program is set, only the steps of simply adding the sample and the like are needed.

The invention is further illustrated below in conjunction with specific Examples. It should be understood that the Examples are provided to illustrate the present invention, but are not intended to limit the scope of the invention. The experimental methods in the following Examples which do not specify the specific conditions are usually in accordance with conventional conditions, such as conditions described in Sambrook et al., Molecular Cloning: Laboratory Manual (New York: Cold Spring Harbor Laboratory Press, 1989), or in accordance with the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight.

The experimental materials involved in the present invention can be obtained commercially unless otherwise specified.

Materials

1. The RNase inhibitor was purchased from TaKaRa. The high-fidelity DNA polymerase KOD FX was purchased from ToYoBo. The primers (oligonucleotides) were synthesized by Shanghai Sangon Biotech. The T7 RNA polymerase was purchased from Thermo. The RNA purification and concentration kit (RNA Clean & ConcentratorTM-5) was purchased from Zymo Research. Wizard® SV Gel and PCR Clean-Up System was purchased from Promega. The media (e.g. Tryptone, Yeast Extract, etc.) were purchased from OXOID.

2. Medium formula: liquid LB (1% Tryptone, 0.5% Yeast extract, 1% NaCl). When formulating solid LB, only 2% agar should be added to the liquid LB.

EXAMPLE 1 Detection of Detectable Single-Stranded DNA Target by Cas12a Proteins (FAM-Labelled Probe)

Single-stranded DNA (target-T1-R) was used as the target sequence to test the response values of different Cas proteins for detection thereof.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-T1-24-R, as shown in table 5, were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen. Biotech.) with a volume of 50-μL, following the annealing program: initial denaturation at 95° C. for 5 min, then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1V per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, RNA is purified using RNA purification and concentration kits, quantitated with NanoDrop 2000C (Thermo Fisher Scientific), diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM Cas12a, 0.01 μM target single-stranded DNA (target-T1-R), 0.01 μM nucleic acid probe (N25-5′ FAM), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. For blank control reaction, all other components were added except single-stranded DNA target sequence. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

3. Fluorescence detection: Electrophoresis was carried out with urea-polyacrylamide gel electrophoresis (Urea-PAGE) and then detection was carried out with the fluorescence luminescence imager. As shown in FIG. 11 , different Cas12as showed distinct target defection effects. For example, HkCas12a and the like cleaved the probe even without target single-stranded DNA being added. However, LbCas12a and the like cleaved the probe only with target single-stranded DNA being added, and were good Cas12a protein candidates.

EXAMPLE 2 Detection of Detectable Single-Stranded DNA Target by Cas12a Proteins (Dural HEX & BHQ1-Labelled Probes)

Single-stranded DNA (target-T1-R) was used as the target sequence to test the response values of different Cas proteins for detection thereof

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-T1-24-R (Table 5) were annealed and used to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM Cas12a, 0.01 μM target single-stranded DNA (target-T1-R), 0.5 μM fluorescent probe (HEX-N12-BHQ1. i.e. 12 nt single-stranded DNA labelled with HEX at the 5′ end and BHQ1 at the 3′ end), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. For control reaction, all other components were added except single-stranded DNA target sequence. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

3. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 12 , different Cas12as showed distinct target defection effects. For example, HkCas12a and the like cleaved the probe even without target single-stranded DNA being added. However, FnCas12a and the like cleaved the probe only with target single-stranded DNA being added, and were good Cas12a protein candidates.

EXAMPLE 3 Detection of Detectable Double-Stranded DNA Target by Cas12a Proteins

Double-stranded DNA (target-T1) was used as the target sequence to test the response values of different Cas12a proteins for detection thereof.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-T1-24-R (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM Cas12a, 0.01 μM target double-stranded DNA (target-T1, obtained from annealing of primer target-T1-F and primer target-T1-R), 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

3. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 7 , different Cas12as showed distinct target defection effects. Whereas LbCas12a and the like cleaved the probe only with target double-stranded DNA being added, and were good Cas12a protein candidates.

EXAMPLE 4 Testing of Targets at Different Concentrations by FnCas12a and LbCas12a

Target-T1 DNA was used as target DNA, then subjected to gradient dilution into different concentrations to test the sensitivity of FnCas12a or LbCas12a response to it. To enhance the sensitivity, PCR amplification step was added.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-T1-24-R (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification (optional): Plasmid (pUC18-T1) that contained the target-T1 target, as the template, was subjected to gradient dilution and PCR reaction. The total volume of each reaction system was 20 μL, 0.25 μM of primers of M13F-47 and M13R-48 ware used (Table 4), and high-fidelity enzyme KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR was completed, the PCR purification products were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM FnCas12a or LbCas12a, 1 μL of PCR products (or target DNA directly diluted to different concentrations), 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 9 , target DNA at or above 0.1 nM was able to response when the test targets were directly added, and response was significant when the concentration was above 1 nM. However, combined with PCR technology, i.e., first PCR amplification of fragments of interest and then Cas12a cleavage reaction, the response sensitivity could be as low as 10 aM.

EXAMPLE 5 Testing of Single-Point Mutation Target by FnCas12a and LbCas12a

Target-T1 DNA was used as the target and mutated in the PAM region and position 1-18, respectively. Several crRNAs of different lengths were tested for response values to the wild type and single-point mutated targets.

1. Preparation of crRNA: First, T7-crRNA-F was annealed with synthetic oligonucleotides of T7-T1-24-R, T7-T1-15-R, T7-T1-16-R, T7-T1-17-R and T7-T1-18-R (Table 5), respectively, to prepare templates for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification: Plasmid (pUC18-T1) that contained the target-T1 target was used as the template. The total volume of each reaction system was 20 μL, 0.25 μM primers of M13R-48 and each mutant primer for Target-T1-F were used (Table 4), and high-fidelity enzyme KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR was completed, they were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM FnCas12a or LbCas12a, 1 μL of PCR products, 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 10 , when the target complementary sequence was 24 nt crRNA (crRNA-24 nt), no significant difference was observed between single-point mutated target with mutation at position 8-18 and the wild type, and after mutation within PAM and at position 1-7, the fluorescence value was obviously decreased. When crRNAs were truncated and the paired target sequence length was 18 nt, the fluorescence value of the mutation at position 8-16 nt was remarkably lower than that at 24 nt. At 16 nt or 17 nt, the fluorescence value of the mutated target sequence was decreased more remarkably. At 15 nt, the fluorescence value of both the target sequences and the mutants was very weak. However, the strength thereof could be still high for other target sequences, which could be used for detection. To sum up, crRNAs of 15 nt, 16 nt and 17 nt were the most suitable for detection of SNP.

EXAMPLE 6 Testing of Microorganisms such as E. coli in Environmental Water

The E. coli gyrB gene was selected as the detection target to indirectly test the concentration of microorganisms such as E. coli in the water. E. coli MG1655 was used as the positive control to determine the content of microorganisms in the environmental water such as polluted water and running water.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-crRNA-gyrB (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification: The positive control sample was E. coil MG1655 which was cultured till the OD₆₀₀ reached about 0.5, then subjected to 10 times gradient dilution and used as the template. Samples were taken from environmental water, including running water and environmental mud water. The total volume of each reaction system was 20 μL, 0.25 μM primers of gyrB-F and gyrB-R were used (Table 4), and high-fidelity enzyme KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR amplification, the PCR products were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from step 1, 0.25 μM LbCas12a, 1 μL of PCR products, 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1, and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 13 , the fluorescence response values were gradually lowered with the decrease of the concentration of E. coli MG1655. Among these, microorganisms were obviously detected in samples 2, 4, 5 and 6.

EXAMPLE 7 Testing of Human SNP

Five sites of human SNP were selected for SNP testing, including rs5082, rs1467558, rs2952768, rs4363657 and rs601338, to test the feasibility of the HOLMES method. 1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1×PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with RNA Clean & Concentrator™-5 (Zymo Research), quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification: The total volume of reaction system was 20 μL, 0.25 μM primers were used (Table 4), 1 ng of human genome (HEK293T) or directly scraped oral mucous epithelium was used as the template, and the high-fidelity polymerase KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR was completed, they were directly used for Cas12a reaction (Primers, such as 1-rs5082-F-T, 2-rs1467558-F-T and 3-rs2952768-R-C were directly introduced into respective mutated products of SNP).

3. Cas12a reaction: In a 20-μL reaction system was added with 1 μM respective crRNA, 0.5 μM LbCas12a, 1 μL of PCR products, and 0.5 μM fluorescent probe (HEX-N12-BHQ1). The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 14 , only with the crRNA corresponding to respective target sequences, higher fluorescence response values were generated, and if one-point mutation occurred, the response value thereof would be largely reduced. The corresponding SNP genotype could be determined based on the fluorescence value, and these results were confirmed by sequencing results.

EXAMPLE 8 Testing of Cancer-Related Genes

TP53 gene was selected for testing gene. TP53 gene contains a nonsense mutation in human T24 cells, which results in the inactivation of this gene. Cells with gene at this site being normal (HEK293T), individual gene and mutated cell T24 were tested.

1. Preparation of crRNA: First, T7-crRNA-F was annealed with synthetic oligonucleotides of T7-crRNA-34-TP53-T24-C-16 nt and T7-crRNA-34-TP53-T24-G-16 nt (Table 5) to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). The crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with RNA Clean & Concentrator™-5 (Zymo Research), quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification: The total volume of reaction system was 20 μL, 0.25 μM primers of 34-TP53-T24-F and 34-TP53-T24-R were used (Table 4), 1 ng of human genome (HEK293T, T24) or directly scraped oral mucous epithelium was used as the template, and the high-fidelity polymerase KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR was completed, they were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 1 μM respective crRNA, 0.5 μM LbCas12a, 1 μL of PCR products, and 0.5 μM fluorescent probe (HEX-N12-BHQ1). The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 15 , when value of crRNA-C detected by using TP53 gene being normal at this site as the template was obviously higher than that of crRNA-G, crRNA-G of the mutated cell T24 was obviously increased.

EXAMPLE 9 Testing of Human SNPs (Gout Related Genes)

Five sites of human SNP were selected for SNP testing, which are related to risk of gout, including rs1014290, rs6449213, rs737267, rs1260326 and rs642803, to test the HOLMES method.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthetized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with RNA Clean & Concentrator TM-5 (Zymo Research), quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator.

2. PCR amplification: The total volume of reaction system was 20 μL, 0.25 μM primers were used (Table 4), 1 ng of human genome (HEK293T) or directly scraped oral mucous epithelium was used as the template, and the high-fidelity polymerase KOD FX (ToYoBo) was used for PCR reaction. The PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s. After PCR was completed, they were directly used for Cas12a reaction. (Primers, such as 1-rs5082-F-T, 2-rs1467558-F-T and 3-rs2952768-R-C were directly introduced into respective mutated products of SNP).

3. Cas12a reaction: In a 20-μL reaction system was added with 1 μM respective crRNA, 0.5 μM LbCas12a, 1 μL of PCR products, and 0.5 μM fluorescent probe (HEX-N12-BHQ1). The reaction was carried out at 37° C. for 15 min, and then stopped at 98° C. for 2 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into the 96-well plate and then detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 16 , only with the crRNA corresponding to respective target sequences, higher fluorescence response values were generated, and if one-point mutation occurred, the response value would be largely reduced. The corresponding SNP genotype could be determined based on the fluorescence value, and the these results were confirmed by sequencing results.

EXAMPLE 10 Testing of the Volunteers' Clinic Samples with Kit SNPs (Gout Related Genes).

Premix was added into the 96-well plate to make a kit, then the genomic DNA of 21 volunteers was added to test the rs1014290 site, which is related to gout risk.

1. Preparation of kit: First, T7-crRNA-F and synthetic oligonucleotides (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthetized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). The RNA was purified with RNA Clean & Concentrator TM-5 RNA (Zymo Research), quantitated with NanoDrop 2000C, and diluted to a concentration of 10 μM.

2. Premix of PCR reagents in the 96-well plate: Reagents required for PCR were added into the 19-μL system, using primers of 41-rs1014290-F and 41-rs1014290-R.

3. Premix in the 96-well plate for fluorescence detection: 1 μM crRNA, 0.5 μM LbCas12a was added into the 19-μL system and 0.5 μM fluorescent probe (HEX-N12-BHQ1) was added into the 96-well plate.

4. PCR amplification: The volunteers' genomic DNA was added into above premixed PCR 96-well plate for PCR reaction, and the PCR reaction procedure was at 95° C. for 2 min, followed by 35 cycles of 98° C. for 10 s, 60° C. for 15 s and 68° C. for 10 s.

5. Cas12a reaction: 1 μL of PCR reaction liquid was added into the premixed 96-well plate for fluorescence detection and reaction was performed at 37° C. for 15 min and then stopped at 98° C. for 2 min.

6. Fluorescence detection: Detection was performed by a microplate reader with the excitation at 535 nm and emission at 556 nm. As shown in FIG. 17 , population with A: A genotype had higher gout risk, so, those except volunteer 5, 7 and 9 who had either A: G or G: G genotypes shall pay more attention to gout risk.

EXAMPLE 11 Detection of Microorganisms Such as E. coli in Environmental Water by LAMP in Combination with Cas Protein

E. coli gyrB gene was chosen as the detection target to indirectly test the presence and absence of microorganisms such as E. coli in water.

1. Preparation of crRNA: First, T7-crRNA-F and synthetic oligonucleotides of T7-crRNA-gyrB (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× Taq DNA polymerase reaction buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthetized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, the RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, finally diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator for later use.

2. LAMP amplification: Sterilized water and liquid polluted with E. coli was taken as the negative control and sample to be detected, respectively. The total volume of each reaction system was 25 μL, 1.6 μM LAMP-FIP and LAMP-BIP primers, 0.2 μM LAMP-F3 and LAMP-B3 primers, and 0.4 μM LAMP-LoopF and LAMP-LoopB primers were used, and WarmStart® LAMP Kit (NEB) was used for LAMP reaction. LAMP reaction procedure was at 65° C. for 30 min. After LAMP was completed, reaction was quenched at 80° C. for 10 min, which were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from Step 1, 0.25 μM Cas12a, 1 μL of LAMP products, 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1 and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into a 96-well plate and detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. The result is shown in FIG. 19 .

EXAMPLE 12 Detection of SNP with LAMP Amplification in Combination with Cas Protein

1. Preparation of crRNA: T7-crRNA-F and synthetic oligonucleotides of T7-crRNA-rs5082-T/T7-crRNA-rs5082-G/T7-crRNA-rs1467558-T/T7-crRNA-rs1467558-C (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× Taq DNA polymerase reaction buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthetized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, the RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, finally diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator for later use.

2. LAMP amplification: Human genomic HEK293T was used as the sample. The total volume of each reaction system was 25 μL, 1.6 μM LAMP-FIP and LAMP-BIP primers, 0.2 0/1 LAMP-F3 and LAMP-B3 primers, and 0.4 μM LAMP-LoopF and LAMP-LoopB primers were used, and WarmStart® LAMP Kit (NEB) was used for LAMP reaction. LAMP reaction procedure was at 65° C. for 30 min. After LAMP was completed, the reaction was quenched at 80° C. for 10 min, which were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from Step 1, 0.25 μM Cas12a, 1 μL of LAMP products, 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1 and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into a 96-well plate and detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. The result is shown in FIG. 20 .

EXAMPLE 13 Detection of Microorganisms such as E. coli in Environmental Water by RPA Amplification in Combination with Cas Protein

E. coli gyrB gene was chosen as the detection target to indirectly test the presence and absence of microorganisms such as E. coli in water.

1. Preparation of crRNA: T7-crRNA-F and synthetic oligonucleotides of T7-crRNA-gyrB (Table 5) were annealed to prepare the template for transcription. Specifically, 4 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 50-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min). crRNA was synthesized using T7 high-yield transcription kit, and the reaction was performed at 37° C. overnight (about 16 h). Then, the RNA was purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, finally diluted to a concentration of 10 ∞M and stored at −80° C. in a refrigerator for later use.

2. RPA amplification: Sterilized water and liquid polluted with E. coli was taken as the negative control and sample to be detected, respectively. The total volume of each reaction system was 25 μL, 0.5 μM RPA-gyrB-F (or RPA-gyrB-F2) and RPA-gyrB-R2 were used as primer, and TwistAmp® Basic Kit (TwistDX) was used for RPA reaction. RPA reaction procedure was at 37° C. for 30 min. After RPA was completed, the reaction was quenched at 80° C. for 10 min, which were directly used for Cas12a reaction.

3. Cas12a reaction: In a 20-μL reaction system was added with 0.5 μM crRNA purified from Step 1, 0.25 μM Cas12a, 1 μL of RPA products, 0.5 μM fluorescent probe (HEX-N12-BHQ1), NEB buffer 3.1 and 0.5 μL of RNA enzyme inhibitor. The reaction was carried out at 37° C. for 15 min.

4. Fluorescence detection: 20 μL of inactivated reaction liquid was added into a 96-well plate and detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. The result is shown in FIG. 21 .

EXAMPLE 14 Cas12b had Collateral Cleavage Activity

1. Preparation of Guide RNA (sgRNA)

First, the plasmid pUC18-guide RNA-T1 with pUC18 as the plasmid backbone was constructed by inserting T7 promoter and the template DNA sequence for transcribing guide RNA into pUC18 (note: the guide RNA transcribed from the template was targeted to the sequence named T1 in the research). The method is as follow: PUC18 plasmid was used as the template with pUC18-1-F and pUC18-1-R as primers for the first round of PCR amplification, and the PCR products were ligated using T4 DNA ligase before being transformed into DH10b. The correct clone was obtained by sequencing, which was named as pUC18-guide RNA-T1-pre. The pUC18-guide RNA-T1-pre was then used as the template for the second round of PCR amplification with pUC18-2-F and pUC18-2-R as primers. In a similar way, the PCR products were ligated and transformed into DH10b, and finally, a correctly sequenced plasmid pUC18-guide RNA-T1 is obtained.

Then, guide RNA was synthetized, using T7 high-yield transcription kit (Thermo), with the plasmid PUC18-guide RNA-T1 as the template. The reaction was performed overnight at 37° C. (12-16 h).

At last, DNase I was added into the transcription system (2 μL of DNase 1 added per 50 μL of the transcription system) and the system was put in 37° C. water bath for 30 min to remove plasmid DNA. The RNA was then purified with an RNA purification and concentration kit, quantitated with NanoDrop 2000C, diluted to a concentration of 10 μM and stored at −80° C. in a refrigerator for later use.

2. Preparation of Target DNA:

(1) If the target DNA is single stranded, a 66-bp oligonucleotide was directly synthesized as the target DNA (target-T1-R), in which the 20-bp target sequence (T1) recognized by guide RNA is contained.

(2) If the target DNA is double stranded, two complementary 66-bp oligonucleotides (i.e. target-T1-F and target-T1-R) were directly synthesized, in which the 20-bp target sequence (T1) recognized by guide RNA is contained. The two oligonucleotides were annealed to obtain target DNA. Specifically, 1 μM of paired oligonucleotides were annealed in 1× PCR buffer (Transgen Biotech) with a volume of 20-μL, following the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. using thermocycler (decrease by 1° C. per min).

3. Cas12b Reaction:

(1) Annealing of guide RNA: guide RNA was diluted to an appropriate concentration (10 μM) and annealed in a PCR instrument, following the annealing procedure: denaturation at 75° C. for 5 min, and then cooling down from 75° C. to 20° C. (decrease by 1° C. per min).

(2) Incubation of guide RNA and C2c1: the annealed guide RNA and the C2c1 of equal molar concentrations were mixed and placed at 30° C. for 20 -30 min.

(3) Cas12b reaction: In a 20-μL reaction system, a mixture of guide RNA and C2c1 (the concentration of both is 250 μM or 500 μM) incubated in Step (2), target DNA (final concentration of 50 nM), FAM-labelled oligonucleotides (target-DNMT1-3-R-FAM-5′) or fluorescence quenching probe (HEX-N12-BHQ1, final concentration of 500 nM), 2 μL of 10× NEB Buffer 3.1 and 0.5 μL of RNA enzyme inhibitor (40 U/μL) were added. After mixing well, they were allowed to react at 48° C. for 30 min. Afterwards, they were heated at 98° C. for 5 min in a PCR instrument for inactivation.

4. Detection of Cas12b for Trans-Cleavage Activity by the Urea Denaturing Gel Electrophoresis Method:

20 μL of inactivated reaction liquid was electrophoretically separated by the urea denaturing gel electrophoresis method, followed by being imaged with the fluorescence imaging system ImageQuant LAS 4000 mini (GE Healthcare). The result is shown in FIG. 22 .

5. Detection of Cas12b for Trans-Cleavage Activity by a Fluorescence Microplate Reader:

20 μL of inactivated reaction liquid was added into a 96-well plate and detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. The result is as shown in FIG. 23 .

EXAMPLE 15 Sensitivity Test of the Trans Reaction (Trans-Cleavage) of Cas12b

Based on the detection of the fluorescence intensity excited by the fluorescence probe (HEX-N12-BHQ1), the target DNA concentration required for Cas12b to perform trans-cleavage activity could be determined, which is the sensitivity of Cas12b trans-cleavage reaction.

1. Preparation of Guide RNA:

First, the 20 bases of the target DNA targeting T1 in the guide RNA were substituted with the guide RNA targeting DNMT1-3 to obtain another plasmid pUC18-guide RNA-DNMT1-3 by PCR, with pUC18-guide RNA-T1 as the template as well as with the guide RNA-DNMT1-3-F and the guide RNA-DNMT1-3-R as primers.

Second, guide RNA was synthesized using the T7 high-yield transcription kit (Thermo), with the plasmid PUC18-guide RNA-DNMT1-3 as the template, the reaction was performed at 37° C. overnight (12-16 h).

At last, DNase I was added into the transcription system (2 μL of DNase I per 50 μL of the transcription system), and was put in a 37° C. water bath for 30 min to remove plasmid DNA, the RNA was then purified with an RNA purification and concentration kit, and then quantitated with NanoDrop 2000C, and stored at −80° C. in a refrigerator for later use.

2. Preparation of Target DNA

For the target DNA, the first method was a reaction system directly added with the Cas12b without amplification, as follows:

(1) if the target DNA is single stranded, a 50-bp oligonucleotide was directly synthesized as the target DNA (DNMT1-3(TTC PAM)-R), in which the 20-bp target sequence (DNMT1-3) recognized by guide RNA is contained.

(2) if the target DNA is double stranded, two complementary 50-bp oligonucleotides (i.e. DNMT1-3 (TTC PAM)-F and DNMT1-3 (TTC PAM)-R)) were directly synthesized, in which the 20-bp target sequence (DNMT1-3) recognized by guide RNA is contained. The two oligonucleotides were annealed to obtain short target DNA. Specifically, the paired oligonucleotides (2 μM) were annealed in 1× PCR buffer (Transgen Biotech) of the total volume 20 μL, followed by performing the annealing procedure: initial denaturation at 95° C. for 5 min, and then cooling down from 95° C. to 20° C. in a thermocycler (decrease by 1° C. per min).

(3) the single stranded or double stranded target DNA was serially diluted to 2 μM, 0.2 μM, 0.02 ∞M, 0.002 μM and 0.0002 μM for later use.

The second method is that a fragment with the target sequence (DNMT1-3) was inserted into a plasmid vector and amplified by LAMP reaction.

(1) The fragment with the target sequence (DNMT1-3) was inserted into the pEasy-Blunt Zero Cloning Vector using the pEasy-Blunt Zero Cloning Kit of Transgen company and verified by sequencing to obtain correct cloning.

(2) LAMP Amplification Reaction

The above plasmids were used as the template for LAMP amplification reaction, and the templates were added with 0 nM, 1 nM, 0.1 nM (diluted to 10⁻¹¹ nM at 10 fold gradient). The total volume of each reaction system was 25-μL, the primers used is 1.6 μM LAMP-DNM-FIP and LAMP-DNM-BIP primers, 0.2 μM LAMP-DNM-F3 and LAMP-DNM-B3 primers, and 0.4 μM LAMP-DNM-LoopF and LAMP-DNM-LoopB, the kit used in the LAMP reaction was WarmStart® LAMP Kit (NEB). LAMP reaction program was at 65° C. for 30 min. After LAMP was completed, quenching at 80° C. for 10 min, and then directly used for Cas12b reaction.

3. Cas 12b Reaction

(1) Annealing of guide RNA: guide RNA was diluted to an appropriate concentration (5 μM), and placed in a PCR instrument for annealing. The annealing procedure: denaturation at 75° C. for 5 min, and then cooling down from 75° C. to 20° C. (decrease by 1° C. per min).

(2) Incubation of guide RNA and Cas12b: the annealed guide RNA and the Cas of equal molar concentration were mixed and placed at 30° C. for 20-30 min.

(3) Cas 12b reaction: in a 20-μL reaction system, a mixture of guide RNA and Cas12b (the concentration of both is 250 μM) incubated in Step (2), 1 μL of target DNA or 1 μL of LAMP products, fluorescence probe (HEX-N12-BHQ1) (final concentration 500 nM), as well as 2 μL of 10× NEB buffer 3.1 and 0.5 μL of RNA enzyme inhibitor (40 U/μL) were added. After mixing well, they were allowed to react at 48° C. for 30 min. Afterwards, they were heated at 98° C. for 5 min in a PCR instrument to quench.

4. Detection of Cas 12b Trans-Cleavage Activity by a Fluorescence Microplate Reader:

20 μL of reaction liquid inactivated was added into a 96-well plate and detected with a microplate reader with the excitation at 535 nm and emission at 556 nm. Upon combining with LAMP amplication, the Cas12b could produce significant collateral ssDNA trans-cleavage activity for as low as 10 aM target DNA. As is shown in FIG. 24 .

The cis cleavage property of Cas12a to cleave target ssDNA:

First, in order to test the ssDNA cleavage property of Cas12a, several crRNAs (Table 1) targeting the short ssDNA (Dfei-3) were designed with 5(6)-carboxyfluorescein (FAM) labelled at the 3′ end. After cleavage of FnCas 12a, the reaction product was analyzed by denatured urea polyacrylamide gel electrophoresis (urea PAGE). Single-stranded DNA cleavage by Cas12a was found to be programmable, i.e., the cleavage site is from the first base in the 3′ end of the target sequence paired with the crRNA guide sequence to near the 22nd base (from 21st to 23rd bases) of the target sequence counted in the 5′ end, as shown in FIGS. 1A and 1C. The dsDNA cleavage of Cas12a requires a PAM sequence, whereas ssDNA cleavage does not require a PAM sequence (FIG. 1A, 1B and FIG. 2 ), which is similar to Cas9-mediated ssDNA cleavage. However, the Cas12a-mediated ssDNA cleavage activity is dependent on the stem-loop structure in crRNA, as shown in FIG. 1A, while Cas9 still exhibits weak cleavage activity against ssDNA with only 20-nt complementary RNA sequences. The stem-loop structure of crRNA is important for stabilizing the structure of Cas12a, which is responsible for the necessity of stem-loop structure of crRNA for ssDNA cleavage of Cas12a. It is further tested whether the ssDNA cleavage site by Cas12a can passed through a shorter guide sequence crRNA, such that the cleavage is outside the recognition site. When the length of the guide sequence is 16 nt, 18 nt or 20 nt, all of these crRNAs resulted in cleavage by Cpf1 near the 22nd base, as shown in FIGS. 1B and 1D, meaning that the cleavage site is 4 nt, 2 nt or 0 nt outside the recognition site. Next, the cleavage efficiency of Cas12a for different substrates was tested using dsDNA and ssDNA substrates, respectively, as shown in FIG. 1F. Similar to the case of Cas9 cleavage, ssDNA cleavage is slower than dsDNA cleavage, as shown in FIG. 1E to 1G. These results indicate that the mechanism of Cas12a's ssDNA recognition and cleavage may be different from dsDNA, which is a less efficient PAM-independent recognition cleavage mode; the PAM sequence accelerates target dsDNA recognition and/or cleavage by Cas12a.

The trans cleavage property of Cas12a to cleave ssDNA:

When the target ssDNA is labelled at the 3′ end, Cas12a cleaves around the 22nd base, as shown in FIG. 1 . However, when the labelling was at the 5′ end, no cleavage product band of the predicted size was observed, but a short (<6 nt) FAM-labelled product was produced, as shown in FIG. 3B. Through detailed experiments, once the ternary complex Cas12a/crRNA/target ssDNA is formed, the 5′-end labelled target ssDNA (DNMT1-3) (Table 1) is cleaved and a short FAM-labelled product is produced, as shown in FIG. 3C. In addition, the ternary complex also cleaves ssDNA that does not have any complementary sequence to the crRNA in any other reaction system (i.e., collateral ssDNA), as shown in FIGS. 3C and 3D. This cleavage phenomenon is a trans cleavage, which is distinguished from a programmable cis cleavage. Trans cleavage was also observed when the target ssDNA was labelled at the 3′-end, but many cis-cleaved products were left, as shown in FIG. 3B, which may be due to the formation of complex Cas12a/crRNA/target ssDNA, which protected the labelled 3′-end of the target ssDNA from being exposed in the active nuclease site of the ternary complex, and these cleavage processes can be shown in FIG. 3A.

In addition to FnCas12a tested above, nine Cas12as from other species source were also tested (Table 2 and FIG. 4A). Except for Lb4Cas12a, all Cas12a have high endonuclease activity on plasmid DNA (as shown in FIG. 4B), and all Cas12a ternary complexes show both cis and trans cleavage activity on ssDNA (as shown in FIGS. 4C and 4D). This suggests that cis and trans activity of Cas12a against ssDNA is a common phenomenon.

Key sites and mechanisms of the cis and trans cleavage of ssDNA by Cas12a

To determine key amino acid residues in Cas12a for cis and trans activity on ssDNA, several candidate residues of Cas12a were mutated for the activity testing. First, three single amino acid mutants of FnCas12a (H843A, K852A and K869A) were purified and tested, the residues of which are related to the RNase activity. The results of the ssDNA trans-activity studies showed that wild-type FnCas12a and three mutants showed no significant difference in cis and trans cleavage activity against ssDNA, as shown in FIGS. 5A and 5C.

Next, when the endonuclease activity site in FnCas12a is mutated, i.e., the RuvC domain (D917A, E1006A or D1255A) and the Nuc domain (R1218A) site, the ssDNA cis and trans-cleavage activity of these mutant Cas12a were affected as shown in FIGS. 5B and 5D. These results indicate that the key sites of Cas12a responsible for target dsDNA cleavage are closely related to the cis and trans cleavage activities of ssDNA.

A recent structural study of Cas12b (i.e. C2c1), including with extended target DNA or extended non-target DNA complexes, revealed that both strands were located within the RuvC pocket, as shown in FIGS. 6A and 6B. By comparing the endonuclease catalyzed residues of Cas (i.e. C2c1) and Cas12a, it is found that these sites most likely to play a similar role in the cleavage and function of Cas12b (i.e. C2c1)and Cas12a. The results of the in vitro single amino acid mutation experiment show that it is consistent with the above hypothesis, that is, Cas12a is likely to cleave both strands by only one RuvC catalytic pocket.

Trans cleavage activity of the Cas12a complex: In the structure of the Cas12b (i.e. C2c1) complex with additional ssDNA, sequence-independent ssDNA is also located on the surface of the catalytic pocket, as shown in FIG. 6C, which is similar to the collateral ssDNA substrate for Cas12a. Combining single amino acid mutation experiments, it is proposed that target DNA, non-target DNA and collateral ssDNA were all cleaved in a single RuvC pocket in Cas12a, as shown in FIGS. 6D, 6E and 6F. The reason why the ternary Cas12a complex has collateral ssDNA trans cleavage activity but the monomeric or binary complex does not have collateral ssDNA trans cleavage activity can be explained by comparing monomeric, binary, and ternary complex structures. The monomeric Cas12a structure is disordered. The binary complex Cas12a/crRNA is a triangular structure, as shown in FIG. 6G, while the ternary complex Cas12a/crRNA/target DNA is converted into a bilobal structure, thereby exposing the catalytic pocket to achieve trans cleavage of the collateral ssDNA (as shown in FIG. 6H).

Establishment of Nucleic Acid Probing Methods

Using the characteristics of Cas12a, a method for specifically detecting nucleic acid molecules has been developed, which is called HOLMES (one Hour Low-cost Multipurpose Efficient Simple assay). As the name of the technology, it is characterized as a one hour, low cost, multi-purpose, efficient, and simple test method.

In the whole reaction system, it can be divided into two large steps. One is the amplification of the template nucleic acid, and the other is the specific nucleic acid detection of the Cas12a protein. Here, PCR is used for amplification of nucleic acids, but in practice, any amplification method can be combined with nucleic acid detection of the second step, such as isothermal amplification method RPA or the like. The initial nucleic acid is not limited to double-stranded DNA, and may be single-stranded DNA; even RNA can be detected by reverse transcription, and thus the method is applicable to various types of nucleic acid molecules. For the nucleic acid detection stage, three components are the key to the experiment, namely Cas12a, crRNA and the nucleic acid probe. In addition to the 10 Cas12a mentioned in the examples (these 10 proteins are randomly selected), other Cas12a proteins are equally suitable for this method. In addition, other types of Cas proteins (such as C2c1 protein) are also suitable for the scope of the present invention. According to experimental results, Alicyclobacillus acidoterrestris Cas12b (i.e. C2c1) also has a collateral single-stranded DNA trans cleavage activity similar to Cas12a, its complex with crRNA/target DNA can also cleave collateral single-stranded DNA.

The crRNA as a guiding role is more stable in the system after being engineered by artificial modification or the like. In the selection of nucleic acid probes, HEX and BHQ1 labelled short single stranded DNA is selected in the present invention, and any other detectable labeling method is theoretically applicable as long as producing a detectable difference after the nucleic acid probe is cleaved. Alternatively, the nucleic acid probe can also be designed to be fluorescent after binding to the compound to probe whether the probe is cut off.

In addition, it should be understood that, after reading the above teachings of the present invention, those skilled in the art may make various modifications and changes to the present invention, these equivalent forms also fall within the scope defined by the claims appended hereto.

TABLE 1 Cas12a property experiment related cleavage substrate sequence Oligo name Sequence (5′-3′) SEQ ID No.: target-DNMT1-3-F aatgtttcctgatggtccatgtctgttactcgcctgtcaagtggcgt  1 gac target-DNMT1-3-R gtcacgccacttgacaggcgagtaacagacatggaccatcagg  2 aaacatt target-DNMT1-3-R- gtcacgccacttgacaggcgagtaacagacatggaccatcagg  3 FAM-3′ aaacatt-FAM target-DNMT1-3-R- FAM-  4 FAM-5′ gtcacgccacttgacaggcgagtaacagacatggaccatcagg aaacatt target-T1-F tttctgtttgttatcgcaactttctactgaattcaagctttactctagaa  5 agaggagaaaggatcc target-T1-R ggatcctttctcctctttctagagtaaagcttgaattcagtagaaagt  6 tgcgataacaaacagaaa target-T1-F-FAM FAM-  7 tttctgtttgttatcgcaactttctactgaattcaagctttactctagaa agaggagaaaggatcc target-T1-R-FAM ggatcctttctcctctttctagagtaaagcttgaattcagtagaaagt  8 tgcgataacaaacagaaa-FAM target-T1-FAM-3′-F tttctgtttgttatcgcaactttctactgaattcaagctttactctagaa  9 agaggagaaaggatcc-FAM target-T1-FAM-5′-R FAM- 10 ggatcctttctcctctttctagagtaaagcttgaattcagtagaaagt tgcgataacaaacagaaa target-DNMT1-3-R- gtcacgccacttgacaggcgagtaacagacatggaccatcagg 11 TTT-FAM-3′ TTTcatt-FAM target-DNMT1-3-R- gtcacgccacttgacaggcgagtaacagacatggaccatcagg 12 CCC-FAM-3′ CCCcatt-FAM target-DNMT1-3-R- gtcacgccacttgacaggcgagtaacagacatggaccatcagg 13 GGG-FAM-3′ GGGcatt-FAM target-DNMT1-3-F- aatgAAAcctgatggtccatgtctgttactcgcctgtcaagtgg 14 AAA cgtgac target-DNMT1-3-F- aatgGGGcctgatggtccatgtctgttactcgcctgtcaagtgg 15 GGG cgtgac target-DNMT1-3-F- aatgCCCcctgatggtccatgtctgttactcgcctgtcaagtgg 16 CCC cgtgac target-T1-1-R acaaacagaaa 17 target-T1-6-R cgataacaaacagaaa 18 target-T1-12-R aagttgcgataacaaacagaaa 19 target-T1-18-R agtagaaagttgcgataacaaacagaaa 20 target-T1-24-R gaattcagtagaaagttgcgataacaaacagaaa 21 target-T1-24-only-R gaattcagtagaaagttgcgataa 22 target-T1-18-only-R agtagaaagttgcgataa 23 target-T1-12-only-R aagttgcgataa 24 target-T1-6-only-R cgataa 25 N25-5′FAM FAM- 26 NNNNNNNNNNNNNNNNNNNNNNNNN N25-3′FAM NNNNNNNNNNNNNNNNNNNNNNNNN- 27 FAM

TABLE 2 Names and GI numbers of Cas12a protein and Cas12b (i.e. C2c1) protein Name GI number Species FnCas12a  489130501 Francisella tularensis AsCas12a  545612232 Acidaminococcus sp. BV3L6 LbCas12a  917059416 Lachnospiraceae bacterium ND2006 Lb5Cas12a  652820612 Lachnospiraceae bacterium NC2008 HkCas12a  491540987 Helcococcus kunzii ATCC 51366 OsCas12a  909652572 Oribacterium sp. NK2B42 TsCas12a  972924080 Thiomicrospira sp. XS5 BbCas12a  987324269 Bacteroidales bacterium KA00251 BoCas12a  496509559 Bacteroidetes oral taxon 274 str. F0058 Lb4Cas12a  769130406 Lachnospiraceae bacterium MC2017 C2c1 1076761101 Alicyclobacillus acidoterrestris

TABLE 3 Plasmid information Plasmids or Strains Relevant properties or genotypes Sources Plasmids pET28a-TEV pET28a with the thrombin (Carneiro, cleavage site changed to the Silva TEV protease cleavage et al. 2006) site pET28a-TEV-FnCas12a pET28a-TEV carrying (Li, Zhao FnCas12a et al. 2016) pET28a-TEV-AsCas12a pET28a-TEV carrying (Li, Zhao AsCas 12a et al. 2016) pET28a-TEV-LbCas12a pET28a-TEV carrying (Lei, Li LbCas12a et al. 2017) pET28a-TEV-Lb5Cas12a pET28a-TEV carrying the present Lb5Cas12a invention pET28a-TEV-HkCas12a pET28a-TEV carrying the present HkCas12a invention pET28a-TEV-OsCas12a pET28a-TEV carrying the present OsCas12a invention pET28a-TEV-TsCas12a pET28a-TEV carrying the present TsCas12a invention pET28a-TEV-BbCas12a pET28a-TEV carrying the present BbCas12a invention pET28a-TEV-BoCas12a pET28a-TEV carrying the present BoCas12a invention pET28a-TEV-Lb4Cas12a pET28a-TEV carrying the present Lb4Cas12a invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present K869A FnCas12a-K869A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present K852A FnCas12a-K852A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present H843A FnCas12a-H843A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present R1218A FnCas12a-R1218A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present E1006A FnCas12a-E1006A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present D917A FnCas12a-D917A invention pET28a-TEV-FnCas12a- pET28a-TEV carrying the present D1255A FnCas12a-D1255A invention pET28a-TEV-C2c1 pET28a-TEV carrying C2c1 the present invention

TABLE 4 Primers used in the HOLMES method test Oligo name Sequence (5′-3′) SEQ ID No.: target-T1-R ggatcctttctcctctttctagagtaaagcttgaattcagtagaaagttg 28 cgataacaaacagaaa M13F-47 cacaattccacacaacatacgagccgga 29 M13R-48 tgtagccgtagttaggccaccacttca 30 Target-T1-F agttttgttatcgcaactttctactgaattc 31 Target-T1-F-1A agttttgAtatcgcaactttctactgaattc 32 Target-T1-F-2A agttttgtAatcgcaactttctactgaattc 33 Target-T1-F-3T agttttgttTtcgcaactttctactgaattc 34 Target-T1-F-4A agttttgttaAcgcaactttctactgaattc 35 Target-T1-F-5G agttttgttatGgcaactttctactgaattc 36 Target-T1-F-6C agttttgttatcCcaactttctactgaattc 37 Target-T1-F-7G agttttgttatcgGaactttctactgaattc 38 Target-T1-F-8T agttttgttatcgcTactttctactgaattc 39 Target-T1-F-9T agttttgttatcgcaTctttctactgaattc 40 Target-T1-F-10G agttttgttatcgcaaGtttctactgaattc 41 Target-T1-AAAN-F aaaagttatcgcaactttctactgaattc 42 Target-T1-F-11A agttttgttatcgcaacAttctactgaattcggtcatag 43 Target-T1-F-12A agttttgttatcgcaactAtctactgaattcggtcatag 44 Target-T1-F-13A agttttgttatcgcaacttActactgaattcggtcatag 45 Target-T1-F-14G agttttgttatcgcaactttGtactgaattcggtcatag 46 Target-T1-F-15A agttttgttatcgcaactttcAactgaattcggtcatag 47 Target-T1-F-16T agttttgttatcgcaactttctTctgaattcggtcatag 48 Target-T1-F-17G agttttgttatcgcaactttctaGtgaattcggtcatag 49 Target-T1-F-18A agttttgttatcgcaactttctacAgaattcggtcatag 50 Target-T1-PAM1A-F agtttAgttatcgcaactttctactgaattc 51 Target-T1-PAM2A-F agttAtgttatcgcaactttctactgaattc 52 Target-T1-PAM3A-F agtAttgttatcgcaactttctactgaattc 53 gyrB-F AGTTGTCGTTCCTCAACTCCGGCGTTTC 54 gyrB-R TCGACGCCAATACCGTCTTTTTCAGTGG 55 1-5082-F CTGCCTTTGCTTCTACCTTTGCCTGT 56 1-5082-F-T TTGCTTCTACCTTTGCCTGTTCTGG 57 1-5082-R TTTTCTGGCTGGGGATGGCCGATGG 58 2-rs1467558-F AGCAATAACACTAATATTGATTCCTTCAG 59 ATATGGACTCCTTTCATAGTA 2-rs1467558-F-T TTGATTCCTTCAGATATGGACTCCTTTCAT 60 AGTATAACG 2-rs1467558-R TGAGCATCGTTATTCTTACGCGTTGTCATT 61 GAAAGAG 3-rs2952768-F AGCCTGGGCAACGAGTGAAACTCTG 62 3-rs2952768-R ACAGGAGGGACAAAGGCCTAAGTGTCC 63 3-rs2952768-R-C CATCATAGGATTGGGAAAAGGACATTTCA 64 GTCATTCAG 4-rs4363657-F AGAGTCCTTCTTTCTCAATTTTTCAGAATA 65 ATTTAGTACTTTGGGTAC 4-rs4363657-R CAGTACTGAAAAAACCTGCCTATCAATAA 66 AAGCCCTAGAC 5-rs601338-F GCTTCACCGGCTACCTTTGCTCCT 67 5-rs601338-R TTCACCTGCAGGCCCCGCAGG 68 34-TP53-T24-F CCTGACTTTCAACTCTGTCTCCTTCCTCTT 69 TTTACAGTA 34-TP53-T24-R TGCTGTGACTGCTTGTAGATGGCCATGG 70 41-rs1014290-F AGTTTCCAGACCTCAGTGCACAAGATACT 71 TTTCTAC 41-rs1014290-F-G ACCTCAGTGCACAAGATACTTTTCTACGT 72 CATCCAC 41-rs101420-R AGCTCCAGTGGATGGAAGATCTTTGAGAT 73 CCAG 42-rs6449213-F AGTCAAAGAGATTCATGCCTGGGACTTTA 74 ATCACATTTAT 42-rs6449213-F-C ATGCCTGGGACTTTAATCACATTTATCGG 75 AAGG 42-rs6449213-R CAAATCTGTCTCCACCTCTCAGCTCACCTT 76 G 43-rs737267-F TTCTTGAACCCAAACTCACCTGGCATTTA 77 AACTG 43-rs737267-F-A AAACTCACCTGGCATTTAAACTGACTCTG 78 TAAG 43-rs737267-F-T AAACTCACCTGGCATTTAAACTGTCTCTG 79 TAAG 43-rs737267-R TGCCGAGGCTGAGTTCAGCTACTCTCC 80 44-rs1260326-F ACACAGCACCGTGGGTCAGACCTTGC 81 44-rs1260326-F-C TGGGTCAGACTTTGCCGGTGAGAGTC 82 44-rs1260326-F-T TGGGTCAGACTTTGCTGGTGAGAGTC 83 44-rs1260326-R AGCAGTGGCCATGTGATGCTGATGATG 84 45-rs642803-F CCCCGGCTCTGTTGGCTTTGAGAATTG 85 45-rs642803-F-C CTCTGTTGGCTTTGAGAATTGCCTGTCTGT 86 GTC 45-rs642803-F-T CTCTGTTGGCTTTGAGAATTGTCTGTCTGT 87 GTC 45-rs642803-R ACCGATACCTGGCAGCCCTTGGATG 88 HEX-N12-BHQ1 HEX-NNNNNNNNNNNN-BHQ1 89

TABLE 5 Template sequences for transcription of crRNA Oligo name Sequence (5′-3′) SEQ ID No.: T7-crRNA-F GAAATTAATACGACTCACTATAGGG  90 T7-T1-24-R gaattcagtagaaagttgcgataaATCTACAACAGTAGAAA  91 TTCCCTATAGTGAGTCGTATTAATTTC T7-T1-15-R agaaagttgcgataaATCTACAACAGTAGAAATTCCCT  92 ATAGTGAGTCGTATTAATTTC T7-T1-16-R tagaaagttgcgataaATCTACAACAGTAGAAATTCCCT  93 ATAGTGAGTCGTATTAATTTC T7-T1-17-R gtagaaagttgcgataaATCTACAACAGTAGAAATTCCC  94 TATAGTGAGTCGTATTAATTTC T7-T1-18-R agtagaaagttgcgataaATCTACAACAGTAGAAATTCC  95 CTATAGTGAGTCGTATTAATTTC T7-crRNA- GAGTAACAGACATGGACCATCAGATCTACAAC  96 DNMT-23 nt-R AGTAGAAATTCCCTATAGTGAGTCGTATTAATT TC T7-crRNA- gacatggaccatcaggaaacattATCTACAACAGTAGAAAT  97 DNMT-(-8)-R TCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- aggcgagtaacagacatggaccaATCTACAACAGTAGAAA  98 DNMT-(+4)-R TTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- tgacaggcgagtaacagacatggATCTACAACAGTAGAAA  99 DNMT-(+8)-R TTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- agacatggaccatcagATCTACAACAGTAGAAATTCCC 100 DNMT-16 nt-R TATAGTGAGTCGTATTAATTTC T7-crRNA- acagacatggaccatcagATCTACAACAGTAGAAATTCC 101 DNMT-18 nt-R CTATAGTGAGTCGTATTAATTTC T7-crRNA- taacagacatggaccatcagATCTACAACAGTAGAAATTC 102 DNMT-20 nt-R CCTATAGTGAGTCGTATTAATTTC T7-DNMT-(-8)- gacatggaccatcaggaaacattCCCTATAGTGAGTCGTAT 103 no loop-R TAATTTC T7-DNMT- aggcgagtaacagacatggaccaCCCTATAGTGAGTCGTA 104 (+4)-no loop-R TTAATTTC T7-DNMT- tgacaggcgagtaacagacatggCCCTATAGTGAGTCGTAT 105 (+8)-no loop-R TAATTTC T7-crRNA- CCTCTTCCCAGAACAGGATCTACAACAGTAGAA 106 rs5082-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- CCTCTTCCCAGCACAGGATCTACAACAGTAGAA 107 rs5082-G ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- CTGAAGCGTTATACTATATCTACAACAGTAGAA 108 rs1467558-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- CTGAAGCGTTGTACTATATCTACAACAGTAGAA 109 rs1467558-C ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- TTTTATCTGAATGATTATCTACAACAGTAGAAAT 110 rs2952768-T- TCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA- TTTTATCTGAATGACTATCTACAACAGTAGAAAT 111 rs2952768-C- TCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA- AAAAAAGAGTGAGTACCATCTACAACAGTAGAA 112 rs4363657-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- AAAAAAGAGTGGGTACCATCTACAACAGTAGAA 113 rs4363657-C ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- GGTAGAAGGTCCAGGAGATCTACAACAGTAGAA 114 rs601338-G ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA- GGTAGAAGGTCTAGGAGATCTACAACAGTAGAA 115 rs601338-A ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-34- GGGCAGGGGAGTACTGATCTACAACAGTAGAAA 116 TP53-T24-C- TTCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA-34- GGGCAGGGGACTACTGATCTACAACAGTAGAAA 117 TP53-T24-G- TTCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA-41- TCAGTGGATGATGTAATCTACAACAGTAGAAAT 118 rs1014290-A- TCCCTATAGTGAGTCGTATTAATTTC 15 nt T7-crRNA-41- TCAGTGGATGACGTAATCTACAACAGTAGAAAT 119 rs1014290-G- TCCCTATAGTGAGTCGTATTAATTTC 15 nt T7-crRNA-42- GGAAATTCTCCTTCCGAATCTACAACAGTAGAA 120 rs6449213-C ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-42- GGAAATTCTCCTTCCAAATCTACAACAGTAGAA 121 rs6449213-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-43- TCTTACAGAGTCAGTTATCTACAACAGTAGAAAT 122 rs737267-A- TCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA-43- TCTTACAGAGCCAGTTATCTACAACAGTAGAAA 123 rs737267-G- TTCCCTATAGTGAGTCGTATTAATTTC 16 nt T7-crRNA-43- GTCTTACAGAGACAGTTATCTACAACAGTAGAA 124 rs737267-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-44- CTGGACTCTCACCGGATCTACAACAGTAGAAAT 125 rs1260326-C- TCCCTATAGTGAGTCGTATTAATTTC 15 nt T7-crRNA-44- CTGGACTCTCACCAGATCTACAACAGTAGAAAT 126 rs1260326-T- TCCCTATAGTGAGTCGTATTAATTTC 15 nt T7-crRNA-45- CACAGACAGGCAATTCTATCTACAACAGTAGAA 127 rs642803-C ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-45- CACAGACAGACAATTCTATCTACAACAGTAGAA 128 rs642803-T ATTCCCTATAGTGAGTCGTATTAATTTC T7-crRNA-gyrB TCGCGCTTGTCGCGCAGACGAATGATCTACAAC 129 AGTAGAAATTCCCTATAGTGAGTCGTATTAATTT C

Primers used in the detection of DNA LAMP amplification in combination with Cas12a:

TABLE 6 Primers for amplifying gyrB-1 name sequence SEQ ID No.: LAMP-gyrB-1-F3 CATGGTGCGTTTCTGGCC 130 LAMP-gyrB-1-B3 CGGCGTTTTGTTCTTGTTCA 131 LAMP-gyrB-1-FIP ACAACTCACGCAGACGTTTCGCAAC 132 CTTCACCAATGTGACCG LAMP-gyrB-1-BIP GTTCCTCAACTCCGGCGTTTCCGAT 133 GCCGCCTTCATAGTGG LAMP-gyrB-1-LoopF CAGAATTTCATATTCGAACT 134 LAMP-gyrB-1-LoopB GACGGCAAAGAAGACCACTT 135

TABLE 7 Primers for amplifying gyrB-2 name sequence SEQ ID No.: LAMP-gyrB-2-F3 CGACGGCAAAGAAGACCA 136 LAMP-gyrB-2-B3 AGCCTGCCAGGTGAGTAC 137 LAMP-gyrB-2-FIP CGGGTGGATCGGCGTTTTGTTCACT 138 ATGAAGGCGGCATCA LAMP-gyrB-2-BIP GTATTGGCGTCGAAGTGGCGTTCGC 139 TGCGGAATGTTGTTG LAMP-gyrB-2-LoopF TTGTTCAGATATTCAACGAACG 140 LAMP-gyrB-2-LoopB GTGGAACGATGGCTTCCAGG 141

TABLE 8 Primers for amplifying the rs 1467558 site name sequence SEQ ID No.: LAMP-rs1467558-F3 CAGCTGTAGACCATAAGCC 142 LAMP-rs1467558-B3 GTGGCTGAGCATCGTTAT 143 LAMP-rs1467558-FIP ACTATGAAAGGAGTCCATATCTGAA 144 GGAATTCAGGTAGTGGTTTGGGA LAMP-rs1467558-BIP GCTTCAGCCTACTGCAAATCCTACG 145 CGTTGTCATTGAAAG LAMP-rs1467558- TCAATATTAGTGTTATTGCTTG 146 LoopF LAMP-rs1467558- TGGTGGAAGATTTGGACAGGAC 147 LoopB

TABLE 9 Primers for amplifying the rs5082 site name sequence SEQ ID No.: LAMP-rs5082-F3 GCTGGAAAGGTCAAGGGAC 148 LAMP-rs5082-B3 GGGGTTTGTTGCACAGTCC 149 LAMP-rs5082-FIP CAAAGGTAGAAGCAAAGGCAGGAG 150 GTTTGCCCAAGGTCACACAG LAMP-rs5082-BIP CTGGGAAGAGGGAGGGCTCAGTGT 151 TGCCACACTTTCACTGG LAMP-rs5082-LoopF GTGAGCGGGTGGGGTGCT 152 LAMP-rs5082-LoopB TCTAAGTCTTCCAGCACGGGATC 153

TABLE 10 Primers used in the detection of RPA amplification in combination with Cas12 SEQ name sequence ID No.: RPA-gyrB- ATATGAAATTCTGGCGAAACGTCTGCG 154 1-F TGAGTTG RPA-gyrB- AAACGTCTGCGTGAGTTGTCGTTCCTC 155 2-F AACTCC RPA-gyrB- ACTTCGACGCCAATACCGTCTTTTTCA 156 R GTGGAG

TABLE 11 Primers used in determination Cas12b for trans cleavage activity: Oligo name Sequence (5′-3′) SEQ ID No.: pUC18-1-F ATCTGAGAAGTGGCACTTATCGCAACTTTCTA 157 CTGAGGTCATAGCTGTTTCCTGTGTGA pUC18-1-R GTCCTCTAGACCCCTATAGTGAGTCGTATTAA 158 TTTCATGATTACGAATTCGAGCTCGGT pUC18-2-F CCACTTTCCAGGTGGCAAAGCCCGTTGAGCTT 159 CTCAAATCTGAGAAGTGGCACTTATC pUC18-2-R TGGAAAGTGGCCATTGGCACACCCGTTGAAA 160 AATTCTGTCCTCTAGACCCCTATAGTGA T7-crRNA-F GAAATTAATACGACTCACTATAGGG 161 ZL-sgRNA-T1-R TCAGTAGAAAGTTGCGATAAGTGC 162 ZLsgRNA- AACAGACATGGACCATCAGGGTG 163 DNMT1-3-R target-T1-F TTTCTGTTTGTTATCGCAACTTTCTACTGAATT 164 CAAGCTTTACTCTAGAAAGAGGAGAAAGGAT CC target-T1-R GGATCCTTTCTCCTCTTTCTAGAGTAAAGCTT 165 GAATTCAGTAGAAAGTTGCGATAACAAACAG AAA target-DNMT1-3- GTCACGCCACTTGACAGGCGAGTAACAGACA 166 R-FAM-5′ TGGACCATCAGGAAACATT target-T1-R GGATCCTTTCTCCTCTTTCTAGAGTAAAGCTT 167 GAATTCAGTAGAAAGTTGCGATAACAAACAG AAA target-T1-F TTTCTGTTTGTTATCGCAACTTTCTACTGAATT 168 CAAGCTTTACTCTAGAAAGAGGAGAAAGGAT CC

TABLE 12 Primers used in the sensitivity test of the trans reaction of Cas12b: Oligo name Sequence (5′-3′) SEQ ID No.: sgRNA-DNMT1-3-F CCTGATGGTCCATGTCTGTTGGTCATAG 169 CTGTTTCCTGTGTG sgRNA-DNMT1-3-R TGGACCATCAGGGTGCCACTTCTCAGAT 170 TTGAGAAG T7-crRNA-F GAAATTAATACGACTCACTATAGGG 171 ZLsgRNA-DNMT1-3-R AACAGACATGGACCATCAGGGTG 172 DNMT1-3(TTC PAM)-F AATGTTCCCTGATGGTCCATGTCTGTTA 173 CTCGCCTGTCAAGTGGCGTGAC DNMT1-3(TTC PAM)-R GTCACGCCACTTGACAGGCGAGTAACA 174 GACATGGACCATCAGGGAACATT LAMP-DNM-F3 gtgaacgttcccttagcact 175 LAMP-DNM-B3 gggagggcagaactagtcc 176 LAMP-DNM-FIP cgccacttgacaggcgagtaactgccacttattgggtcagc 177 LAMP-DNM-BIP gcgtgttccccagagtgacttagcagcttcctcctcctt 178 LAMP-DNM-LoopF aggaaacattaacgtactgatg 179 LAMP-DNM-LoopB ttecttttatttcccttcagc 180 DNMT1-3(TTC PAM)-R GTCACGCCACTTGACAGGCGAGTAACA 181 GACATGGACCATCAGGGAACATT DNMT1-3(TTC PAM)-F AATGTTCCCTGATGGTCCATGTCTGTTA 182 CTCGCCTGTCAAGTGGCGTGAC

TABLE 13 Other sequences involved in the present invention Name Sequence SEQ ID No.: AacCas12b sgRNA GTCTAGAGGACAGAATTTTTCAACGGGTGTG 183 sequence CCAATGGCCACTTTCCAGGTGGCAAAGCCCG TTGAGCTTCTCAAATCTGAGAAGTGGCACcctg atggtccatgtctgtt Guide sequence cctgatggtccatgtctgtt 184 targeting target DNMT-1-3 Single-stranded gtcacgccacttgacaggcgagtaacagacatggaccatcagggaacatt 185 target sequence Double-stranded gtcacgccacttgacaggcgagtaacagacatggaccatcagggaacatt 186 target sequence: amino acid MAVKSIKVKLRLDDMPEIRAGLWKLHKEVNA 187 sequence of GVRYYTEWLSLLRQENLYRRSPNGDGEQECDK AacCas12b protein TAEECKAELLERLRARQVENGHRGPAGSDDEL LQLARQLYELLVPQAIGAKGDAQQIARKFLSPL ADKDAVGGLGIAKAGNKPRWVRMREAGEPG WEEEKEKAETRKSADRTADVLRALADFGLKPL MRVYTDSEMSSVEWKPLRKGQAVRTWDRDMF QQAIERMMSWESWNQRVGQEYAKLVEQKNRF EQKNFVGQEHLVHLVNQLQQDMKEASPGLESK EQTAHYVTGRALRGSDKVFEKWGKLAPDAPFD LYDAEIKNVQRRNTRRFGSHDLFAKLAEPEYQ ALWREDASFLTRYAVYNSILRKLNHAKMFATF TLPDATAHPIWTRFDKLGGNLHQYTFLFNEFGE RRHAIRFHKLLKVENGVAREVDDVTVPISMSEQ LDNLLPRDPNEPIALYFRDYGAEQHFTGEFGGA KIQCRRDQLAHMHRRRGARDVYLNVSVRVQS QSEARGERRPPYAAVFRLVGDNHRAFVHFDKL SDYLAEHPDDGKLGSEGLLSGLRVMSVDLGLR TSASISVFRVARKDELKPNSKGRVPFFFPIKGND NLVAVHERSQLLKLPGETESKDLRAIREERQRT LRQLRTQLAYLRLLVRCGSEDVGRRERSWAKL IEQPVDAANHMTPDWREAFENELQKLKSLHGI CSDKEWMDAVYESVRRVWRHMGKQVRDWR KDVRSGERPKIRGYAKDVVGGNSIEQIEYLERQ YKFLKSWSFFGKVSGQVIRAEKGSRFAITLREHI DHAKEDRLKKLADRIIMEALGYVYALDERGKG KWVAKYPPCQLILLEELSEYQFNNDRPPSENNQ LMQWSHRGVFQELINQAQVHDLLVGTMYAAF SSRFDARTGAPGIRCRRVPARCTQEHNPEPFPW WLNKFVVEHTLDACPLRADDLIPTGEGEIFVSPF SAEEGDFHQIHADLNAAQNLQQRLWSDFDISQI RLRCDWGEVDGELVLIPRLTGKRTADSYSNKV FYTNTGVTYYERERGKKRRKVFAQEKLSEEEA ELLVEADEAREKSVVLMRDPSGIINRGNWTRQ KEFWSMVNQRIEGYLVKQIRSRVPLQDSACENT GDI*

All publications mentioned in the present invention are incorporated by reference as if each individual publication was cited as a reference in the present application. It should be understood that, after reading the above teachings of the present invention, those skilled in the art can make various modifications and changes to the present invention. These equivalent forms are also within the scope defined by the claims appended hereto. 

1. A method for detecting target nucleic acid molecules, characterized by adding a guide RNA, a Cas protein, a nucleic acid probe and a buffer into the system containing the target nucleic acid molecules to be detected, and then detecting the nucleic acid probe.
 2. The method for detecting target nucleic acid molecules of claim 1, characterized in that the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a; the Cas12a is preferably one of FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a or Lb4Cas12a; the Cas12a is preferably LbCas12a.
 3. The method for detecting target nucleic acid molecules of claim 1, characterized in that the guide RNA refers to an RNA that directs the Cas protein to specifically bind to the target DNA.
 4. The method for detecting target nucleic acid molecules of claim 1, characterized in that the nucleic acid probe is a single-stranded DNA; the single-stranded DNA is preferably a fluorescently labelled single-stranded DNA; and the single-stranded DNA is preferably a fluorescent probe labelled with a fluorescent group HEX at the 5′ end and a quenching group BHQ1 at the 3′ end; preferably, the detection method of the nucleic acid probe is preferably a fluorescence detection method; and the fluorescence detection method is preferably detection method using a microplate reader or a fluorescence spectrophotometer.
 5. The method for detecting target nucleic acid molecules of any one of claims 1 to 4, characterized in that the target nucleic acid molecules to be detected in the reaction system of the target nucleic acid molecules to be detected are obtained by amplification.
 6. The method for detecting target nucleic acid molecules of claim 5, characterized in that the detection method can detect pathogenic microorganisms, gene mutations or specific target DNA.
 7. The method of claim 1, characterized in that the Cas protein comprises Cas12b (i.e., C2c1).
 8. A use of a Cas protein in a method for detecting target nucleic acid molecules.
 9. The use of claim 8, characterized in that when the target DNA, the guide RNA and the Cas protein form a ternary complex, the complex cleaves other single-stranded DNA molecules in the system; preferably, the guide RNA refers to RNA that directs the Cas protein to specifically bind to the target DNA.
 10. A kit for detecting target nucleic acid molecules, characterized in that the kit comprises a guide RNA, a Cas protein, and a nucleic acid probe.
 11. A detection system for detecting target nucleic acid molecules, characterized in that the system comprises: (a) a Cas protein, which is Cas12a or a Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a; (b) a guide RNA, which directs the Cas protein to specifically bind to target nucleic acid molecules; and (c) a nucleic acid probe, which is a single-stranded DNA; wherein the target nucleic acid molecule is a target DNA.
 12. The detection system of claim 11, characterized in that the Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a is selected from the group consisting of: Cas12b (i.e., C2c1).
 13. The detection system of claim 11, characterized in that the nucleic acid probe comprises a single-stranded DNA with a detectable label.
 14. A kit for detecting target nucleic acid molecules, characterized in that the kit comprises: i) a first container and a Cas protein located in the first container, the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-strand DNA cleavage activity of Cas12a; ii) optionally a second container and a guide RNA located in the second container, the guide RNA directs the Cas protein to specifically bind to the target nucleic acid molecules; iii) a third container and a nucleic acid probe located in the third container; and iv) optionally a fourth container and a buffer located in the fourth container; wherein the target nucleic acid molecule is a target DNA.
 15. A method for detecting the presence or absence of target nucleic acid molecules in a sample, characterized by comprising the steps of: (a) providing a detection system for detecting target nucleic acid molecules according to claim 11, and the detection system further contains a sample to be detected; and (b) detecting whether the nucleic acid probe in the detection system is cleaved by the Cas protein, the cleavage is a trans-cleavage of the collateral single-stranded DNA; wherein, if the nucleic acid probe is cleaved by the Cas protein, it indicates that the target nucleic acid molecule is present in the sample; and if the nucleic acid probe is not cleaved by the Cas protein, it indicates that the target nucleic acid molecule is not present in the sample.
 16. The method of claim 15, characterized in that the nucleic acid amplification method is selected from the group consisting of: PCR amplification, LAMP amplification, RPA amplification, ligase chain reaction, branched DNA amplification, NASBA, SDA, transcription-mediated amplification, rolling circle amplification, HDA, SPIA, NEAR, TMA and SMAP2.
 17. The method of claim 15, characterized in that, when the PAM sequence is absent at the upstream or downstream of the target site (in the range of from −20 nt to +20 nt, preferably in the range of from −15 nt to +15 nt, more preferably in the range of from −10 nt to +10 nt), nucleic acid amplification was carried out using primers introduced with PAM.
 18. The method of claim 17, characterized in that the primer introduced with PAM has a structure of formula I from 5′ to 3′: P1-P2-P3   (I) wherein, P1 is a 5′ segment sequence complementary or non-complementary to the sequence of the target nucleic acid molecule at the 5′ end; P2 is a PAM sequence; and P3 is a 3′ segment sequence complementary to the sequence of the target nucleic acid molecule at the 3′ end.
 19. The method of claim 15, characterized in that, when the PAM sequence is present at the upstream or downstream of the target site (in the range of from −20 nt to +20 nt, preferably in the range of from −15 nt to +15 nt, more preferably in the range of from −10 nt to +10 nt), primers with or without a PAM sequence can be used, and the amplified amplification product contains the PAM sequence.
 20. A use of a Cas protein, characterized by being used for the preparation of a detection reagent or kit for detecting target nucleic acid molecules based on a collateral single-stranded DNA cleavage, wherein the Cas protein is Cas12a or a Cas protein having an activity similar to the collateral single-strand DNA cleavage activity of Cas12a.
 21. The use of claim 20, characterized in that the Cas protein having an activity similar to the collateral single-stranded DNA cleavage activity of Cas12a is selected from the group consisting of: Cas12b (or C2c1).
 22. A method for detecting target nucleic acid molecules comprising steps of: (a) providing a mixture including: a Cas12 protein having collateral cleavage activity; a guide RNA operative with the Cas12 protein; a detectably labeled nucleic acid probe susceptible to the collateral cleavage activity; a buffer; and a system in which target nucleic acid molecules are to be detected; and (b) detecting cleavage of the nucleic acid probe.
 23. The method of claim 22, wherein the guide RNA specifically binds to the target nucleic acid molecule(s).
 24. The method of claim 22, wherein the Cas12 protein is selected from the group consisting of: FnCas12a, AsCas12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a, Lb4Cas12a; LbCas12a and Cas12b (i.e., C2c1).
 25. The method of claim 22, wherein the target nucleic acid molecules to be detected have been amplified.
 26. The method of claim 25, wherein the target nucleic acid molecules have been amplified by a method selected from the group consisting of: PCR amplification, LAMP amplification, RPA amplification, ligase chain reaction, branched DNA amplification, NASBA, SDA, transcription-mediated amplification, rolling circle amplification, HDA, SPIA, NEAR, TMA and SMAP2.
 27. The method of claim 25, wherein the target nucleic acid molecules have been amplified using primers comprising a PAM sequence.
 28. The method of claim 27, wherein the amplification product comprises a PAM sequence upstream or downstream of the guide RNA's target site.
 29. The method of claim 28, wherein the PAM site is −20 nt to +20 nt upstream or downstream of the target site.
 30. The method of claim 22, wherein the nucleic acid is detectably labeled with a fluorescent label.
 31. The method of claim 30, wherein the fluorescent label comprises a fluorescent group HEX at the 5′ end and a quenching group BHQ1 at the 3′ end.
 32. The method of claim 22, wherein detecting cleavage of the nucleic acid probe comprises detecting fluorescence.
 33. The method of claim 30, wherein the step of detecting fluorescence comprises using a microplate reader or a fluorescence spectrophotometer.
 34. A combination comprising: a Cas12 protein having collateral cleavage activity; a guide RNA operative with the Cas12 protein and directed to a sequence in a target nucleic acid; a detectably labeled nucleic acid probe; and a buffer.
 35. The combination of claim 34, further comprising a sample in which the target nucleic acid is to be detected. 